The present invention relates in general to semiconductor manufacture, and more particularly, to systems and methods for determining overlay error and correction in the manufacture of semiconductor devices by lithographic techniques using a lithographic apparatus.
Semiconductor device manufacturing involves depositing multiple layers of patterned materials on a substrate. All of these multiple patterned layers must be aligned correctly in order for any of the devices to operate properly. Any variations in alignment are generally referred to as overlay errors, which can be measured using metrology in order to determine whether two layers on a substrate are aligned or not. Minimizing overlay errors is important for achieving high yield and reliability, and for ensuring that devices meet performance specifications. Any devices outside the tolerances for overlay will need to be reworked, which is costly and time consuming.
To build the complex structures that make up a transistor and the many wires that connect the millions of transistors of a circuit, lithography and etch pattern transfer steps are repeated at multiple times. Each pattern being printed on the wafer is aligned to the previously formed patterns and slowly the conductors, insulators, and selectively doped regions are built up to form the final device. A typical semiconductor device can include twenty to thirty levels of patterned layers. The placement of the patterned features on a given level must match the placement of corresponding features on other levels within an accuracy that is some fraction of the minimum feature size or critical dimension (CD). Generally, as the device features scale downwards and pattern density increases, overlay error budgets also shrink. Because of this, conventional multi-exposure and multi-patterning schemes require very tight overlay error budgets. In conventional lithographic systems, various alignment mechanisms are provided to align features in a given layer to the features in an underlying layer. For advanced nodes, however, optical or extreme ultraviolet (EUV) scanner improvements alone do not reduce the overlay error enough to meet the required specifications.